The invention relates to pumps in general, and more particularly to improvements in peristaltic pumps. Still more particularly, the invention relates to improvements in peristaltic pumps of the type wherein an annular diaphragm of elastically deformable material is installed in a housing and can be displaced against the internal surface of the housing to thereby cause a fluid to flow from an inlet to an outlet of the housing.
German Pat. No. 29 11 609 to Becker discloses a peristaltic diaphragm pump wherein a rotary piston is caused to roll along the internal surface of a sleeve-like section of the diaphragm to thereby urge successive increments of the sleeve-like section against the internal surface of the housing. The sleeve-like section and the internal surface of the housing define an annular pumping chamber which communicates (at least at times) with the inlet and the outlet. A radially outwardly projecting extension of the diaphragm is anchored in the housing between the inlet and the outlet. That portion of the sleeve-like section which is integral with the extension is stiffer than the remaining portion of the sleeve-like section. This causes the piston to induce vibrations, especially when it is caused to orbit in the sleeve-like section of the diaphragm at an elevated speed, i.e., when it travels along the extension at a high frequency. It could be said that the piston runs out of true because it is caused to depart from its prescribed path whenever it reaches the junction of the sleeve-like section with the extension.
German Pat. No. 28 53 916 to Becker discloses a modified peristaltic diaphragm pump wherein the junction between the sleeve-like section and the extension of the diaphragm is provided with a recess which is bounded by a concave surface and is intended to reduce the resistance of the junction to deformation by the piston which is caused to roll along the internal surface of the sleeve-like section. This contributes to complexity of the diaphragm but does not eliminate vibration, especially when the piston is caused to roll at a high speed, i.e., when it travels over the junction at a high or very high frequency.
It is necessary to ensure that the piston move successive increments of the sleeve-like section of the diaphragm into pronounced sealing engagement with the internal surface of the housing. This is particularly important if the pump is to convey a gaseous fluid because such mode of operation ensures that the pump is self priming. Thus, it is necessary to ensure that the peripheral surface of the rolling piston deform the adjacent portion of the sleeve-like section, i.e., such portion of the section must be deformed against the adjacent portion of internal surface of the housing. Furthermore, the thickness of the sleeve-like section must be selected with a view to ensure that the diaphragm can compensate for manufacturing and other tolerances. The result is that the sleeve-like section is squeezed between the piston and the housing. This is highly undesirable because squeezing or crushing of the diaphragm brings about pronounced fulling and prevents the pump from operating smoothly, quietly and without rapid destruction of the diaphragm. Moreover, the energy requirements of the means for rolling the piston along the internal surface of the sleeve-like section of the diaphragm are high. Attempts to provide the diaphragm with a relatively thin sleeve-like section have failed, mainly because this further shortens the life expectancy of the diaphragm.